The present invention relates to a method for correcting the signal delivered by an angular position sensor, more specifically suited to such a sensor comprising a Hall-effect cell past which the teeth of a target of the toothed wheel type pass.
Motor vehicles frequently make use of devices that measure the position and/or the rotational speed of rotating shafts, these devices consisting of sensors sensitive to the passage of the teeth of a toothed wheel, generally made of ferromagnetic material, secured to the rotating shaft. These sensors may be based on the principle of variable reluctance or, more recently, on the use of one or more Hall-effect cells. The latter make it possible to detect variations in magnetic flux which are generated by the passage of a magnetized tooth (if the sensor has no permanent magnet generating a reference magnetic flux) or a ferromagnetic tooth when the cell is associated with a permanent magnet, and thus deliver a rectangular electric signal representative of the passage of the teeth. These devices are encountered, for example, in the measurement of the position or speed of the crankshaft or camshaft in internal combustion engines, or alternatively in the measurement of the rotational speed of the wheels of the vehicle.
It has, however, been found that the electric signal delivered by these sensors was not an exact representation of the passage of the teeth past the sensor. What happens is that the rising and falling fronts of the electric signal may occur with a slight phase shift with respect to the precise passage of the rising or falling flank of the teeth of the target past the sensor, it being possible for this phenomenon to be attributed to the influence, in certain configurations, of the approach or retreat of the metal mass represented by the teeth with respect to the lines of flux passing through the Hall-effect cell. While this phase shift has only very little impact on applications such as the measurement of the rotational speed of a wheel of the vehicle, where it is essentially the period of the signal that is of interest, the same is not true of applications that make use of the rising and falling fronts of the signal in order to determine the position of a camshaft such as, for example, in applications aimed at measuring the camshaft timing with respect to top dead center in one cylinder in engines equipped with variable camshaft timing devices.
It is therefore an object of the present invention to propose a method that makes it possible to measure the phase shift between the electric signal delivered by the sensor and the actual mechanical position of the teeth passing past it, and in doing so, to correct this signal.
These objects of the invention, together with others which will become apparent in what follows of the present description, are achieved by means of a method for correcting the signal of a camshaft position sensor, said sensor delivering a rectangular signal corresponding to the passage of teeth and of hollows of a target secured to an engine camshaft whereby:
In a first embodiment of the method, the angular values of the alternations of the signal corresponding to the teeth and to the hollows are evaluated, these angular values are compared with the mechanical angles of the teeth and of the hollows, and from this a phase shift of the rising and falling fronts of the signal with respect to the corresponding flanks of the teeth of the target is deduced.
According to a first alternative form of this embodiment, the angular values of the alternations of the signal are evaluated by measuring the duration of said alternations as a function of the rotational speed of the engine.
Advantageously, evaluation may be performed over a period for which the engine is running at constant speed, or alternatively, the duration measurement may be corrected for the influences of a variation in speed by measuring at least two consecutive pairs of teeth/hollows.
According to another alternative form of this embodiment, the angular values of the alternations of the signal are evaluated on the basis of angular information delivered by a position sensor associated with a target secured to the engine crankshaft.
In a second embodiment of the method, which is applicable when said teeth and hollows extend over equal angular sectors, a phase shift of the rising and falling fronts of the signal with respect to the corresponding flanks of the teeth of the target is calculated by comparing duration measurements of two consecutive alternations of the signal.
Advantageously, in this embodiment too, the duration measurements may be made during a period for which the engine is running at constant speed, or may alternatively be corrected for the influences of a variation in speed by measuring at least two consecutive pairs of teeth/hollows.